Sound cards and processors on motherboards in today's new computers are commodity items: Unless you go out of your way to find a cheap one, you can expect the audio controller supplied with your system to provide entirely adequate performance for listening to music in two-channel stereo from CDs, movie soundtracks on DVDs, and streaming audio from the Internet. The quality you hear depends on the quality of the original recording or the bandwidth of the Internet feed, but you can generally expect the sound through your computer to be at least as good as a local FM radio station or a decent CD player.
The basic feature set includes:
Stereo (two-channel) recording and playback
Analog line-level input
Analog output for stereo speakers
Minimum CD quality (16-bit/44.1 KHz) bit rate
Many motherboards and sound cards have additional features that build on that minimum. These include:
Surround sound outputs (at least 5.1, which means five speakers plus a subwoofer)
Digital inputs and outputs that bypass the ADC and DAC converters
Support for DVD movies
96 KHz or 192 KHz maximum sampling rate
24-bit bit depth
MIDI (Musical Instrument Digital Interface) input for connecting keyboards and other instruments to the computer
Support for 2-D and 3-D audio in games and other accelerated video
Some audio engineers believe that a sound controller inside a computer case, on either a motherboard or an expansion card, should never be used for serious recording because the computer's power supply and other components can produce electronic noise. Therefore, many professional recording interfaces are in a separate enclosure that connects to the computer through a USB or Firewire port.
The Sound Blaster range of sound cards made by Creative Technology has been the dominant brand in consumer-level audio controllers for many years. As a result, some salespeople describe controllers on motherboard and sound cards from other manufacturers as "Sound Blaster compatible."
In fact, Sound Blaster cards have evolved and improved over time, so it's entirely possible for a competing card to be "Sound Blaster compatible" because it matches the features and functions of an old and long-obsolete Sound Blaster model; but that's no guarantee that it's as good as a current-model Sound Blaster (or a current card from some other company).
The real standard for sound controllers in personal computers is the joint Intel-Microsoft PC 2001 System Design Guide that includes the technical guidelines for expansion cards and peripheral devices that work with Windows (you can download a copy from http://www.microsoft.com/whdc/system/platform/pcdesign/desguide/pcguides.mspx, but it's not particularly exciting reading). Any new sound controller you're likely to find probably exceeds the Design Guide's specifications, so there is no longer any reason to worry about whether or not a sound card is "Sound Blaster compatible."
As I said earlier in this chapter, the sound controllers supplied with most new computers are fine for day-to-day listening and occasional recording, but like everything else attached to a computer, it's also possible to replace them with high-end versions that offer improved performance. Like just about everything else inside your computer, one of the most common reasons to buy one of those high-end sound controllers is to play the latest generation of computer games. However, high-end audio cards also have some other uses.
High-quality sound controllers fall into several quite different categories: sound cards for games, surround sound for home entertainment systems, and interfaces for professional-quality recording. Each of these applications requires a specific type of audio product; it's not possible to install an all-purpose, high-end sound controller.
As you know, many new games place extremely heavy demands on a computer's CPU, RAM, and other components. Audio is no exception, so a sound card designed specifically for games enhances the game-playing experience.
The design goals for a game-player's sound card include:
2-D and 3-D positional effects that create the illusion of individual sounds coming from specific directions that may track the images on one or more screens. The best positional audio effects work either through speakers or headphones.
A DSP that offloads as much audio processing as possible from the CPU.
Dedicated audio RAM that leaves more system memory for other activity.
High definition (24-bit) audio conversion to enhance sound quality.
The objective of a modern home theater system is to reproduce the experience of watching a movie in a theater, with speakers located all around the seats. Unlike a concert hall (or traditional two-channel stereo) where the sound is spread across an aural stage in front of the listener, a surround sound system places you right in the middle of the action.
Surround sound requires at least four speakers (two in front and two in back), but the most common setups add a fifth center-front speaker. In addition, most surround systems include a separate speaker for very low frequencies called a subwoofer. A system with five main speakers and a sub-woofer is identified as a 5.1 system. Some systems also add a pair of side speakers between front and rear to create 7.1 sound.
Therefore, an audio controller for a surround sound system has enough output connections for all of the main speakers. These might be separate sockets for each speaker or a big multi-pin plug that mates to a special breakout cable.
Many DVDs and audio files include soundtracks already encoded for surround sound; a surround sound audio controller can also synthesize surround sound from a file with only two channels.
For serious recording, a sound controller must create and store digital audio files that are the most accurate possible copies of the original analog or digital source material. Those sources can include an amplifier, a microphone connected directly to the sound card, or the analog or digital output of a mixing desk. The same sound card's outputs are often used to convey digital audio from the computer to a professional environment such as a radio station or a recording studio.
To accomplish this, a professional-quality recording interface usually has these features:
Balanced analog input and output channels that are less sensitive to hum and noise
Very low internal noise and distortion
High sample rates and bit rates (at least 24-bit/96 kHz)
Digital inputs and outputs
Support for the ASIO (Audio Stream In/Out) specification for multi-channel recording
Clock synchronization with digital inputs
Flexible control software (see Figure 13.1)
Figure 13.1: The control software for a professional audio interface offers many options and settings.
The alternative to an internal sound controller is an audio interface in a separate enclosure that exchanges data with the CPU through a USB or Firewire port. An external sound controller can be anything from a simple adapter like the one shown in Figure 13.2 that simply converts input signals to digital format and passes it to the computer, to the full-featured mixing desk in Figure 13.3 that includes multiple microphone and high-level inputs, audio equalization and many other features.
Figure 13.2: An external sound controller can be quite simple …
Figure 13.3: … or extremely complex.
External sound controllers can offer these benefits:
Lower exposure to hum and noise generated inside the computer case
Hardware controls for input and output channels
Higher-quality microphone channels and other audio circuits
More flexible operation